Because blending "hip" elements of "mainstream music" makes western music more "cool" and "appealing" to casuals, blending zimmer-style guitars into everything has been a long-standing Western tradition for the past decade or so. Unfortunately, it's usually very poorly implemented, and is partly what gives way to the whole copy-cat fiasco surrounding Zimmer.

While a few exceptions still exist in the west, it is from the east that we see the best blends occurring between the genres. DMC's style of music should be nothing unfamiliar to most visitors of this site, while the composer behind Fairy Tail and Towards the Terra often implements rock elements often into his music. Another notable is Chaos Legion.

Adding metal instruments or other rock elements to your insert genre here soundtrack is a very conscious decision, one that should never be taken lightly and never done so just because it sounds "cool". In DMC and other notables it works because that is the overall style of the game and the prose. Throwing electric guitars into the composition just for the hell of it generally just comes off as poorly thought out and destroys the immersion. Thankfully for DMC this style, when it works, is exactly what the ARPG genre can make use of.

In the first song, the death metal fits well as it produces a very heavy atmosphere (or energy in your case), which was released exponentially by the pinch of acoustics every loop. In the second, the acoustics themselves were chosen and tuned to portray the chaotic nature of the death metal it selves, so they fits snuggly into each other.

That being said, Russians and Ukrainians are the only kind of people in the world toi have at taste of music.